1. Field of the Invention
The present invention relates to a fuel injection pump for an internal combustion engine (hereinafter referred to as "the engine").
2. Description of Related Art
One type of known radial pump has plural plungers radially provided at an outer periphery of a cam, and pressurizes fuel sucked into fuel pressurizing chambers formed on respective plungers. According to the radial pump, in general, pressure feed fuel passages for transferring high pressure fuel pressurized in the fuel pressurizing chambers are united together in a pump housing, and the fuel is supplied to a common-rail from the united pressure feed fuel passage.
However, when the plural pressure feed fuel passages are united in the pump housing to form one pressure feed fuel passage, the pump housing gets a corner portion at the united portion of the pressure feed fuel passage. Since a fuel injection pump for a common-rail-type diesel engine may pressurize fuel up to about 200 MPa, stress caused by fuel pressure concentrates on the corner portion of the pump housing to cause a damage on the corner portion if the corner portion is formed on an inner peripheral wall of the pump housing which forms the pressure feed fuel passage ("the inner peripheral wall of the pump housing which forms the pressure feed fuel passage" is called "passage inner peripheral wall" hereinafter).
Further, when the housing is drilled to form the pressure feed fuel passage, a corner portion is formed on the passage inner peripheral wall after drilling. If the stress caused by the fuel pressure concentrates on the corner portion, the passage inner peripheral wall other than the united portion may be damaged.
In order to prevent the stress concentration on the corner portion of the passage inner peripheral wall caused by the fuel pressure, a thin electrode may be inserted in the pressure feed fuel passage to discharge between the corner portion of the passage inner peripheral wall and the electrode thereby rounding the corner portion, or the corner portion may be polished to remove the corner portion by introducing a fluid including an abrasive material. However, the removal of the corner portion is difficult because the passage length becomes longer when the pressure feed fuel passages are directly united together in the pump housing.
Furthermore, reducing the size of the fuel injection pump has been requested according to the request for reducing engine in size to improve the fuel economy. However, it is difficult to reduce the fuel injection pump in size when the pressure feed fuel passages are united in the pump housing because the pump housing becomes bigger. Further, the weight of the fuel injection pump increases since a hard metal, such as iron, is used for the pressure feed fuel passage. Furthermore, an installation location of a large fuel injection pump is restricted by interference with an engine and engine peripheral components.